In conventional elevators, a shaft was usually provided for each elevator and one car was housed in one shaft. Therefore, in a case where a plurality of elevators are installed, shafts for the number of elevators were juxtaposed and hence each car could ascend and descend freely without interfering with other cars. In such an installed condition, a plurality of elevators were subjected to group control for an improvement in transportation efficiency.
Incidentally, in a high-rise building where a large number of elevators are installed, installing a shaft for each car posed the problem that the ratio of the area of the shaft portion to the floor area of the building is too high.
Therefore, to reduce the area of the shaft portion, in Japanese unexamined laid-open patent publication No. 2000-226164, for example, there is disclosed an apparatus for elevator group control in which a plurality of cars are brought into service within the same shaft, and when a hall call is registered, whether a retreat is necessary is judged by calculating the mutual interference of the cars. When a retreat is necessary, by causing cars other than assigned cars to retreat, the mutual interference of the cars is prevented thereby to respond to the hall call.
In the apparatus for elevator group management described in the above-described Japanese unexamined laid-open patent publication No. 2000-226164, however, although the ratio of the area of the shaft portion to the floor area of the building is reduced, the upper car and the lower car compete with each other in the assignment of a hall call because the upper car and the lower car use almost the entire zone of the shaft as a common service zone with the exception of terminal floors. For this reason, the unassigned cars must be in retreat in order not to impede the operation of the assigned cars, thus posing the problem that the transportation efficiency decreases.
Furthermore, in Japanese unexamined laid-open patent publication No. 6-305648, there is disclosed a multicar type elevator system in which the two top portions and two bottom portions of two shafts are each connected by a horizontal shaft to form annular shafts and a plurality of cars are housed in these annular shafts to permit circulation in a specific direction. In this elevator system, when a succeeding car enters into a prescribed distance from a preceding car in the travel direction, the succeeding car is stopped thereby to prevent a collision.
However, in a circulation type elevator, when the elevator is to go to a floor in a direction reverse to the circulation direction although a destination floor is near in terms of distance, the elevator must almost make one round in a circulation path. In particular, an elevator in which a plurality of cars are housed in one shaft is to be installed in a high-rise building and, therefore, taking a round in the above-described circulation path means that the elevator takes a round between the lowest floor of the building and the highest floor thereof. For this reason, the circulation type elevator poses the problem that much time is taken and the transportation efficiency is low. In order to solve this problem, it is also conceivable to juxtapose elevators which circulate in the reverse direction. However, this posed the new problem of excessive equipment.
The present invention was made to solve the above-described problems and has as its object the provision of an apparatus for elevator group control which avoids mutual interference of a set or multiple sets of elevators consisting of an upper car and a lower car which are disposed in a vertical relation within one elevator shaft and which ascend and descend independently, and which also improves transportation efficiency.